You should add into this thread Optix, and The Living Room as both are Royal Caribbean Teen Concepts. I'll comment on the Voyager, Freedom and Sovereign Class.
The Sovereign class of ships have just recently recieved their Fuel upgrades. Previously, the Sovereign of the Seas had no teen center (pre-04) and the Monarch and Majesty had Fantaseas Teen Center which was located far too close to the Adventure Ocean facilities. Now, its my understanding that all of the ships have been outfitted with the Fuel/Living Room Combo. RCI's Ships either have Fuel AND The Living Room OR Optix which is a combination. After a recent cruise on the Sovereign of the Seas, the clubs are small but a LOAD of fun and the director on my ship was the best i've had in my cruise history.
Fuel is commonly regarded as the "night club" and includes a state-of-the-art sound and light system in addition to a bar serving Coke products and Mocktails (non-alcoholic specialty drinks).
The Living Room is the "chill zone" and has a variety of pieces of cool furniture, tables, games and activities like foosball tables. The Living Room also has a bar on some ships.
The Voyager Class (Eagle Class) Ships also have been outfitted with teen facilities. The Voyager, Explorer and Adventure of the Seas feature Optix Teen Disco, located on Deck 12 Aft. Optix is a concept developed for ships with expanded Adventure Ocean facilities and combines the concept of Fuel and The Living Room and features the light and sound system in addition to couches, activities and a bar. The Mariner and Navigator of the Seas have both Fuel and The Living Room, located on Deck 12 Aft. The space in which Fuel resides on these 2 ships is occupied by Adventure Beach (kiddy pool & slide) on the Earlier Voyager Class ships.
The Freedom Class Ships feature facilities pretty much IDENTICAL to that of the Mariner and Navigator of the seas. While I can't comment on the Liberty or Independence of the Seas as I haven't yet traveled on them, the Freedom of the Seas is identical all the way down to the carpet in both Fuel and The Living Room, which is only slightly bigger on the FOTS.
All of Royal Caribbean's teen facilities include some form of Club Cafe', an internet zone for teens that offers a reduced rate of $.25 per minute for internet access versus the $.50 fee in Royal Caribbean Online. Keep in mind, however, that you get what you pay for and in my experience, the internet in the teen zones is much slower than in Royal Caribbean Online.